Permeability and roughness determinations of wax-hydrocolloid coatings, and their limitations in determining citrus fruit overall quality

Water vapor, O-2 and CO2 permeability of wax-hydrocolloid (xanthan, locust bean gum or guar) coatings were determined in custom-made apparatuses. Because the formulations do not, have a 'body' of their own, they were uniformly smeared on cellulose and low-density polyethylene for WVP and gases permeability determinations, respectively, by speedball hard-rubber brayer. The permeances were calculated and used to estimate the permeabilities of the coatings. No statistical differences were observed between water vapor permeabilities of xanthan-, guar- and locust bean gum-containing coatings and a commercial coating for citrus fruit. For O-2 and CO2, all coatings were less permeable than the commercial one. These results could lead to the assumption that wax-hydrocolloid-coated citrus fruits suffer from considerable ethanol and acetaldehyde buildup, as well as that of off-flavors. However, the wax-hydrocolloid-coated fruits were, in fact, tasty due to disturbances in the smooth coating and less blockage of stomata. The average roughness of the wax-hydrocolloid coatings was slightly (but not statistically) higher than that of the commercial one. The added hydrocolloids caused the structure of the coating to be less ordered. Although no visible difference in wax-flake appearance was detected, their size as a result of gum addition was much smaller: thus, the hydrocolloid either coats the wax flakes and eliminates their continuous layer structure or helps limit their growing process from a grain or small flake to a uniform, undisturbed coating layer. (C) 2001 Elsevier Science Ltd. All rights reserved.